Oxygenator

ABSTRACT

An oxygenator which helps avoid bubbles in the blood from being discharged through the blood outlet port of the oxygenator includes a housing, a hollow fiber membrane bundle in the housing and formed by a multiplicity of hollow fiber membranes serving for gas exchange, gas-inlet and gas-outlet ports communicating with gas passages of the hollow fiber membranes, and a blood-inlet and blood-outlet ports. A filter member is provided on a side closer to the blood outlet port of the hollow fiber membrane bundle and serves to catch bubbles in blood. The blood outlet port projects from the housing and a passage enlargement is provided in a vicinity of the end of the blood outlet port closer to the housing and having an increased passage cross-sectional area. The blood passed the filter member is allowed to reach the blood outlet port by being decelerated in the passage enlargement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/655,126filed on Jan. 19, 2007 which claims priority to Japanese Application No.2006-011705 filed on Jan. 19, 2006, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to oxygenators.

BACKGROUND DISCUSSION

There are known oxygenators constructed to perform gas exchange by useof a multiplicity of hollow fiber membranes. U.S. Pat. No. 6,503,451describes an example of such an oxygenator.

This oxygenator includes a housing, a hollow fiber membrane bundlereceived in the housing, blood-inlet and blood-outlet ports, andgas-inlet and gas-outlet ports so that gas exchange, i.e. oxygenationand carbon dioxide removal, is performed between the blood and gasthrough the hollow fiber membranes.

In oxygenators, it is possible for bubbles to exist in the blood comingentering the blood inlet port. In such a case, bubbles should preferablybe removed by the hollow fiber membrane bundle.

However, the hollow fiber membrane bundle is designed to efficientlyeffect gas exchange and is not specifically designed or intended toremove bubbles. Thus, a problem exists in that bubbles are not fullyremoved by the hollow fiber membrane bundle. As a result, bubblesremaining in the blood are discharged out of the blood outlet port andcarried with the blood downstream of the oxygenator. For this reason, itis a known practice to provide an arterial filter on an arterial linebetween the oxygenator and the patient for purposes of removing bubbles.

SUMMARY

An oxygenator comprises a housing having an interior, a blood inlet portin the housing through which blood is adapted to flow, with the bloodinlet port opening to outside the housing and communicating with theinterior of the housing to introduce the blood into the interior of thehousing, a hollow fiber membrane bundle positioned in the interior ofthe housing and comprised of a multiplicity of integrated hollow fibermembranes configured to subject the blood introduced into the housing togas exchange, with the hollow fiber membranes each possessing a lumenextending between opposite ends of the hollow fiber membrane forming agas passage for passage of gas, and a gas inlet port in the housingthrough which gas is adapted to flow, with the gas inlet port opening tooutside the housing and communicating with the gas passages of thehollow fiber membranes to introduce the gas into the gas passages. A gasoutlet port in the housing through which gas is adapted to flow opens tooutside the housing and communicates with the gas passages of the hollowfiber membranes to discharge the gas in the gas passages, and a bloodoutlet port in the housing through which blood which has been subjectedto the gas exchange is adapted to flow opens to outside the housing andcommunicates with the interior of the housing to discharge from thehousing the blood which has been subjected to the gas exchange. A filtermember is positioned at a side of the hollow fiber membrane bundlecloser to the blood outlet port and is constructed to catch bubbles inthe blood which has been subjected to the gas exchange, and a passageenlargement is provided in a vicinity of an end of the blood outlet portcloser to the housing and possessing an increased passagecross-sectional area so that blood which has passed through the filtermember toward the blood outlet port is decelerated in the passageenlargement.

Because blood is decelerated in the passage enlargement, the bubblestrapped by the filter are prevented from being carried in blood to theblood outlet port. The bubbles in the blood can thus be prevented fromgoing out of the blood outlet.

According to another aspect, an oxygenator comprises a housing having aninterior, a blood inlet port in the housing through which blood isadapted to flow, with the blood inlet port opening to outside thehousing and communicating with the interior of the housing to introducethe blood into the interior of the housing, a hollow fiber membranebundle positioned in the interior of the housing and comprised of amultiplicity of integrated hollow fiber membranes configured to subjectthe blood introduced into the housing to gas exchange, wherein thehollow fiber membranes each possess a lumen extending between oppositeends of the hollow fiber membrane forming a gas passage for passage ofgas, a gas inlet port in the housing through which gas is adapted toflow, with the gas inlet port opening to outside the housing andcommunicating with the gas passages of the hollow fiber membranes tointroduce the gas into the gas passages, a first gas outlet port in thehousing through which gas is adapted to flow, with the first gas outletport opening to outside the housing and communicating with the gaspassages of the hollow fiber membranes to discharged the gas in the gaspassages, and a blood outlet port in the housing through which bloodwhich has been subjected to the gas exchange is adapted to flow, whereinthe blood outlet port opens to outside the housing and communicates withthe interior of the housing to discharge from the housing the bloodwhich has been subjected to the gas exchange. A bubble filter member ispositioned at a side of the hollow fiber membrane bundle closer to theblood outlet port and is constructed to catch bubbles in the blood whichhas been subjected to the gas exchange, and a gas outlet hollow fibermembrane layer is positioned between the hollow fiber membrane bundleand the filter member, with the gas outlet hollow fiber membrane layercomprising a multiplicity of hollow fiber membranes each possessing alumen. A second gas outlet port in the housing through which bubblesremoved by the filter member gas are adapted to flow opens to outsidethe housing and communicates with the lumens of the hollow fibermembranes forming the gas outlet hollow fiber membrane layer todischarge the bubbles.

In accordance with another aspect, a method of performing gas exchangefor blood comprises introducing blood into a housing in which arepositioned a plurality of hollow fiber membranes each having a lumen sothat the blood flows exteriorly of the hollow fiber membranes,introducing gas into the lumens of the hollow fiber membranes to subjectthe blood flowing exteriorly of the hollow fiber membranes to gasexchange with the has flowing through the lumens of the hollow fibermembranes, removing bubbles in the blood while the blood is in thehousing and after the blood has been subjected to the gas exchange,decelerating the blood from which bubbles have been removed as the bloodapproaches a blood outlet port in the housing, and discharging the bloodwhich has been decelerated from the housing by way of the blood outletport.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective view of a first embodiment of an oxygenatordisclosed herein.

FIG. 2 is a cross-sectional side view of the oxygenator shown in FIG. 1taken along the section line II-II in FIG. 1.

FIG. 3 is a top view partly in cross-section of the oxygenating part ofthe oxygenator shown in FIG. 1.

FIG. 4 is an enlarged cross-sectional view of a lower right region(fixing region of the hollow fiber membrane bundle, filter member andgas outlet hollow fiber membrane layer) of the oxygenator shown in FIG.2;

FIG. 5 is a cross-sectional side view of a second embodiment of anoxygenator.

FIG. 6 is a plan view of a third embodiment of an oxygenator with aportion of the housing body removed.

FIG. 7 is a left side or end view of the oxygenator shown in FIG. 6 asviewed along the arrow VII-VII in FIG. 6.

FIG. 8 is a cross-sectional view of the oxygenator shown in FIG. 7 takenalong the section line VIII-VIII in FIG. 7.

FIG. 9 is a cross-sectional view of the oxygenator taken along thesection line IX-IX in FIG. 7.

FIG. 10 is a cross-sectional view taken along the section line X-X inFIG. 6.

FIG. 11 is an enlarged cross-sectional view of an upper right region(fixing region of a hollow fiber membrane bundle, filter member and gasoutlet hollow fiber membrane layer) in FIG. 9.

FIG. 12 is a cross-sectional view of a fourth embodiment of anoxygenator.

FIG. 13 is a cross-sectional side view of a fifth embodiment of anoxygenator.

FIG. 14 is a cross-sectional side view of a sixth embodiment of anoxygenator.

FIG. 15 is a cross-sectional view of a seventh embodiment of anoxygenator.

FIG. 16 is a perspective view of a cylindrical housing body of theoxygenator shown in FIG. 15.

FIG. 17 is a cross-sectional view of an eighth embodiment of anoxygenator.

FIG. 18 is a cross-sectional view of a ninth embodiment of anoxygenator.

FIG. 19 is a cross-sectional view of a tenth embodiment of anoxygenator.

FIG. 20 is a cross-sectional view of a cylindrical housing body of anoxygenator in a comparative example.

DETAILED DESCRIPTION

FIGS. 1-4 illustrate various features associated with one disclosedembodiment of an oxygenator as disclosed herein. In FIGS. 1 and 2, theupper side is referred to as “upper” or “above”, the lower side isreferred to as “lower” or “below”, the left side is referred to as“blood inlet side” or “upstream side”, and the right side is referred toas “blood outlet side” or “downstream side”.

The oxygenator 1 in the illustrated embodiment is a heatexchanger-equipped oxygenator that includes an oxygenating part 1Aadapted to perform gas exchange on blood and a heat exchanging part(heat exchanger) 1B adapted to perform heat exchange on blood. Thisoxygenator can be set up on a blood extracorporeal circulation circuit,for example.

The oxygenator 1 comprises a housing 2 located on the side of theoxygenating part 1A, and a housing 5 located on the side of the heatexchanger part 1B. The two housings 2, 5 are united or integratedtogether as a single unitary body.

The housing 2 of the oxygenator part 1A is comprised of a cylindricalhousing body 21 quadrilateral (rectangle or square) in cross-section(hereinafter, referred to as a “rectangular cylindrical housing body”),a first header (upper lid) 22 that closes the upper opening of therectangular cylindrical housing body 21, and a second header (lower lid)23 that closes the lower opening of the rectangular cylindrical housingbody 21. Both the first header 22 and second header 23 are dish-shaped,including a plate-shaped portion with a projecting or upstanding wallextending around the periphery of the plate-shaped portion.

The rectangular cylindrical housing body 21, the first header 22 and thesecond header 23 can each be formed of a resin material, e.g. polyolefinsuch as polyethylene or polypropylene, an ester resin (e.g. polyestersuch as polyethylene terephthalate or polybutylene terephthalate), astyrene resin (e.g. polystyrene, MS resin or MBS resin) orpolycarbonate, ceramics materials of various kinds or a metal material.The first and second headers 22, 23 are secured in a liquid-tight mannerto the rectangular cylindrical housing body 21 by joining, for exampleby fusion or an adhesive.

The rectangular cylindrical housing body 21 is formed with a tubularblood outlet port 28 projecting from the lower region of the bloodoutlet side thereof. A passage enlargement 281 possessing a box-shapedform is provided around the blood outlet port 28 closer to therectangular cylindrical housing body 21 (housing 2), i.e., at and aroundthe upstream end of the blood outlet port 28. The blood outlet port 28has a lumen in communication with the interior (a lumen) of the passageenlargement 281, thus forming a passage through which the blood whichhas passed through a filter member 41, described in more detail below,is to pass. As shown in FIGS. 2 and 3, the passage enlargement 281 isprovided as a region where the passage increases in cross-sectional arearelative to the blood outlet port 28.

In the oxygenator 1, the blood passing through the filter member 41reaches the blood outlet port 28 in a state in which the blood has beendecelerated by the passage enlargement 281.

A tubular gas inlet port 26 projects from the upper surface of the firstheader 22. A tubular gas outlet port 27 and a tubular gas outlet port 29project from the lower surface of the second header 23. The gas inletport 26 has an intermediate portion that is bent nearly perpendicularlyso that the tip end portion of the gas inlet port 26 is parallel withthe blood outlet port 28.

It is to be understood that the housing 2 need not necessarily be aperfect rectangular parallelepiped in form over its entirety in that itmay be chamfered or rounded partly or entirely at corners or may be in aform partly cut away or added with a different-shaped part.

Positioned in the housing 2 is a hollow fiber membrane bundle 3 formedby integrating a multiplicity of hollow fiber membranes 31 whichfunction to carry out gas exchange, a filter member 41 serving as bubbleremoval means 4 provided on the blood outlet port 28 (blood outletportion) side of the hollow fiber membrane bundle 3, and a gas outlethollow fiber membrane layer 42, as shown in FIGS. 2-4. The hollow fibermembrane bundle 3, the filter member 41 layers and gas outlet hollowfiber membrane layer 42 are arranged in that order, with the hollowfiber membrane bundle 3 being located closer to the blood inlet side.

As shown in FIG. 4, almost all the hollow fiber membranes 31 forming thehollow fiber membrane bundle 3 are arranged nearly parallel with oneanother. In this case, the lengthwise direction of the hollow fibermembranes 31 are arranged vertically.

Incidentally, the arrangement pattern, direction, etc. of the hollowfiber membranes 31 of the hollow fiber membrane bundle 3 are not limitedto those mentioned but may be, for example, in a structure in which thehollow fiber membranes 31 are arranged horizontally, a structure inwhich the hollow fiber membranes 31 obliquely intersect one another atintersections, a structure in which all or some of the hollow fibermembranes 31 are arranged curved, or a structure in which all or some ofthe hollow fiber membranes 31 are arranged in a corrugated, helical,spiral or annular manner.

The hollow fiber membranes 31 have opposite ends fixed to the innersurfaces of the rectangular cylindrical housing body 21 by way ofpartitioning walls 8, 9 as shown in FIG. 2. The partitioning walls 8, 9are formed of a potting material, e.g. polyurethane or silicone rubber.

The hollow fiber membrane bundle 3 has opposite ends, in the widthwisedirection, that are respectively fixed (secured) to the inner surfacesof the rectangular cylindrical housing body 21 through a setting member7 as shown in FIG. 3. The setting member 7 may be formed of a materialsimilar to the material (potting material) of the partitioning wall 8, 9or of another material.

A first chamber 221 is defined by the first header 22 and thepartitioning wall 8. The first chamber 221 is divided, by way of apartition 222, into a gas inlet chamber 261 closer to the hollow fibermembrane bundle 3 and a small space 223 closer to the gas outlet hollowfiber membrane layer 42. The partition 222 is positioned, relative to aside-to-side direction (left-to-right direction in FIG. 2), in aboundary between the hollow fiber membrane bundle 3 and the gas outlethollow fiber membrane layer 42. The hollow fiber membranes 31 haverespective upper openings in communication with the gas inlet chamber261.

A second chamber 231 is also defined by the second header 23 and thepartitioning wall 9. The second chamber 231 is divided, by way of apartition wall 232, into a gas outlet chamber 271 closer to the hollowfiber membrane bundle 3 and a small space 233 closer to the gas outlethollow fiber membrane layer 42. The partition 232 is positioned,relative to a side-to-side direction (left-to-right direction in FIG.2), in a boundary between the hollow fiber membrane bundle 3 and the gasoutlet hollow fiber membrane layer 42. The hollow fiber membranes 31have respective lower openings in communication with the gas outletchamber 271 as shown in FIG. 4.

The hollow fiber membranes 31 each have a lumen forming a gas passage 32through which gas is adapted to flow. The gas inlet port 26 and the gasinlet chamber 261 constitute a gas inlet portion in communication withthe gas passages 32 at an upstream end of the gas passages. The gasoutlet port 27 and the gas outlet chamber 271 constitute a gas outletportion in communication with the gas passages 32 at a downstream end ofthe gas passages.

The hollow fiber membrane bundle 3 is fully positioned in therectangular cylindrical housing body 21 and is sized and configured insuch a way that the hollow fiber membrane bundle 3 possesses arectangular parallelepiped form and occupies a majority of the space inthe housing body interior.

The hollow fiber membranes 31 are exposed between the partitioning walls8, 9, within the housing 2. A blood passage 33 is formed exterior of thehollow fiber membranes 31 (and also the gas outlet hollow fibermembranes 421 discussed in more detail below). That is, a the bloodpassage 33 exists at gaps between the hollow fiber membranes 31,allowing the blood to flow from left to right in FIG. 2.

A blood inlet aperture (blood inlet space) 24 is formed as a blood inletportion at the upstream end of the blood passage 33 (at the upstream endof the hollow fiber membrane bundle 3 in a side-to-side direction). Theblood inlet aperture 24 communicates with the blood passage 33 andpossesses an elongated (e.g., strip-shaped) form extending vertically(nearly parallel with the longitudinal extent of the hollow fibermembranes 31). The blood inlet aperture 24 is formed in a connectionbetween the rectangular cylindrical housing body 21 and the heatexchanger housing 5. Thus, the interior of the housing 2 is incommunication with the interior of the heat exchanger housing 5, throughthe blood inlet aperture 24. This structure allows for a relativelyefficient transfer of blood from the heat exchanging part 1B to theoxygenating part 1A.

The blood inlet aperture 24 preferably has a length (vertical length asseen with reference to FIG. 2) equal to or greater than 70% of theeffective length of the hollow fiber membrane 31 (i.e., the lengthbetween the lower face of the partitioning wall 8 and the upper face ofthe partitioning wall 9), with the length of the blood inlet aperture 24preferably being no greater than the effective length of the hollowfiber membrane 31. In the illustrated embodiment, the length of theblood inlet aperture 24 is equal to the effective length of the hollowfiber membrane 31. This disclosed length of the blood inlet aperture 24allows for relatively efficient transfer of blood from the heatexchanging part 1B to the oxygenating part 1A and for gas exchange ofblood in the blood passage 33.

At least at the upstream end of the blood passage 33 (closer to theblood inlet aperture 24), the blood flows in a direction orthogonal tothe lengthwise extent of the hollow fiber membranes 31. This allows forrelatively efficient gas exchange of the blood flowing through the bloodpassage 33.

At the downstream end of the blood passage 33 closer to the downstreamportion of the hollow fiber membrane bundle 3, a gap is formed between afilter member 41 (described in more detail below) and the inner surfaceof the rectangular cylindrical housing body 21. The gap is located wherethe blood which has passed through the filter member 41 is to flow, thusforming a blood outlet aperture (blood outlet space) 25. A blood outletportion is formed by the blood outlet aperture 25, the passageenlargement 281 and the blood outlet port 28 communicating with theblood outlet aperture 25 though the passage enlargement 281. The bloodoutlet aperture 25 or gap has a constant width-wise dimensionrepresented as “t.”

With the blood outlet aperture 25, the blood outlet portion is providedwith a space where the blood transmitted through the filter member 41flows toward the blood outlet port 28, thus discharging the bloodrelatively smoothly.

The hollow fiber membrane bundle 3, the filter member 41, the gas outlethollow fiber membrane layer 42 and the blood passage 33 are positionedbetween the blood inlet aperture 24 and the blood outlet aperture 25.

By way of example, the hollow fiber membranes 31 is made of a porousgas-exchange film. Also by way of example, the porous hollow fibermembranes can possess an inner diameter of approximately 100-1000 μm, awall thickness of approximately 5-200 μm, more preferably 10-100 μm, aporosity of approximately 20-80%, more preferably approximately 30-60%,and a pore size of approximately 0.01-5 μm, more preferablyapproximately 0.01-1 μm.

The hollow fiber membrane 31 can be made of a hydrophobic polymermaterial, e.g. polypropylene, polyethylene, polysulfone,polyacrylonitrile, polytetrafluoroethylene or polymethyl pentane.Polyolefin resin is preferred, and polypropylene is more preferred.Pores are preferably formed in the wall of the material by, for example,stretching or solid-liquid phase separation.

The hollow fiber membranes 31 of the hollow fiber membrane bundle 3 havea length (effective length) that is not particularly limited, but ispreferably approximately 30-150 mm, more preferably approximately 50-100mm.

Similarly, the thickness of the hollow fiber membrane bundle 3(horizontal length or dimension in FIG. 2) is not specifically limited,though is preferably approximately 10-100 mm, more preferablyapproximately 20-80 mm.

The width of the hollow fiber membrane bundle 3 (vertical dimension orlength in FIG. 3) is also not particularly limited, but is preferablyapproximately 10-100 mm, more preferably approximately 20-80 mm.

As described previously, a bubble removal means 4 is provided at aposition downstream of the hollow fiber membrane bundle 3 (closer to theblood outlet portion). The bubble removal means 4 functions to catchbubbles in blood and discharge the caught bubbles to the outside of theblood passage. The bubble removal means 4 comprises a filter member 41and a gas outlet hollow fiber membrane layer 42 arranged upstream of thefilter member 41. The filter member 41 catches bubbles existing in theblood flowing along the blood passage 33. The gas outlet hollow fibermembrane layer 42 is formed by integrating a multiplicity of gas outlethollow fiber membranes 421 (hereinafter referred to as hollow fibermembranes 421) which transmit and discharge the bubble-forming gascaptured at the filter member 41. In the description below, the gas thatforms the bubbles caught at the filter member 41 is referred to as“bubble gas”.

The filter member 41 is formed by a flat sheet member nearly in arectangular form (hereinafter also referred to as a “sheet”). The filtermember 41 is fixed in the housing 2 by being secured at its edges (foursides) through use of the partitioning walls 8, 9 and the respectivesetting members 7.

The filter member 41 is positioned by placing its one surface in contactwith the downstream surface portion (closer to the blood outlet portion)of the gas outlet hollow fiber membrane layer 42, thus covering nearlyall the surface portion. The filter member 41 thus has an increasedeffective area so that it is possible to relatively fully exhibit thecapability of catching bubbles. Also, by increasing the effective areaof the filter member 41, even if clogging (e.g., adhesion of bloodaggregates) occurs in a part of the filter member 41, it is possible toinhibit or prevent the filter member 41 from being wholly obstructed toblood flow.

The filter member 41 may be, for example, in a mesh form or of a wovenfabric, a non-woven fabric or a combination thereof. Of these, a meshform for the filter member 41 is preferred, particularly a screenfilter. This makes it possible to catch bubbles more positively and topass blood relatively easily.

In the case of the filter 41 being in a mesh form, the mesh size is notlimited but is usually preferably 80 μm or smaller, more preferablyapproximately 15-60 μm, further preferably 20-45 μm. This makes itpossible to catch comparatively fine bubbles without increasing thepassage resistance to blood, thus providing a quite high catchefficiency of bubbles (i.e., bubble removal capability).

The filter member 41 can be made of a material, e.g. polyolefin such aspolyamide, polyethylene or polypropylene, polyester such as polyethyleneterephthalate, or polybutylene terephthalate, nylon, cellulose,polyurethane, or an aramid fiber. It is preferable to use polyethyleneterephthalate, or polyethylene, polyurethane due to its relativelyexcellent resistance to blood clotting and the capability of being lessclogged.

Meanwhile, the filter member 41 preferably possesses hydrophilicity.That is, the filter member 41 is preferably made itself of a hydrophilicmaterial or has been subjected to a hydrophilizing processing (e.g.plasma processing). This makes it relatively easy to remove bubbles uponpriming the oxygenator 1. Also, when blood mixed with bubbles passesthrough, it is difficult for the bubbles to pass through, thus improvingthe bubble removal capability at the filter member 41 and helpingpositively prevent or inhibit the bubbles from flowing out of the bloodoutlet port 28.

The filter member 41 may be made of one sheet (particularly, a mesh formlike a screen filter) or a lamination of two or more sheets. In the caseof a lamination of two or more sheets, the sheets forming the filtermember are preferably different in at least one of the conditions oftheir forms, the material(s) forming the sheets, the mesh sizes of thesheets, the flatness/non-flatness of the sheets, the plan shapes of thesheets, etc.

As mentioned, between the filter member 41 and the interior surface ofthe housing 2, a gap (i.e., blood outlet aperture 25) is formed as shownin FIGS. 2-4). This can help suppress the filter member 41 from cominginto direct (close) contact with the inner surface of the housing 2.Thus, the blood passing through the filter member 41 is allowed toeasily flow down the blood outlet aperture 25, and then to the bloodoutlet port 28 relatively smoothly via the passage enlargement 281.

The filter member 41 should preferably closely contact the gas outlethollow fiber membrane layer 42.

With the arrangement of the filter member 41, even where bubbles existin the blood flowing along the blood passage 33, such bubbles can becaught thereby inhibiting or preventing bubbles from going out of theblood outlet port 28. This reduces or eliminates the need for anarterial filter conventionally provided in the arterial line.

The bubbles caught by the filter member 41 are removed by the gas outlethollow fiber membrane layer 42 located upstream of the filter member 41(located between the filter member 41 and the hollow fiber membranebundle 3).

As shown in FIG. 4, the hollow fiber membranes 421 forming the gasoutlet hollow fiber membrane layer 42, are arranged nearly parallel withthe hollow fiber membranes 31 forming the hollow fiber membrane bundle3. The hollow fiber membranes 421 have both ends (upper and lower ends)fixed to the inner surfaces of the rectangular cylindrical housing body21 by way of the partitioning walls 8, 9 as shown in FIG. 2, similar tothe hollow fiber membranes 31.

Thus, both ends of both the hollow fiber membranes 421 and the hollowfiber membranes 31 can be fixed by way of the partitioning walls 8, 9.The number of process steps can thus be reduced in the manufacture of anoxygenator 1. In addition, the hollow fiber membranes 421 can be fullypositioned within the rectangular cylindrical housing body 21. That is,a high charging efficiency of the hollow fiber membranes 421 isavailable in the rectangular cylindrical housing body 21 (with less deadspace). This contributes to the size reduction and performanceimprovement of the oxygenating part 1A.

As shown in FIG. 3, the gas outlet hollow fiber membrane layer 42 isfixed (secured) at both of its widthwise ends to the inner surfaces ofthe rectangular cylindrical housing body 21 by the setting members 7.

The hollow fiber membranes 421 each have a lumen forming a gas passage422 through which is adapted to flow bubble gas entering through amultiplicity of fine pores formed in the wall of the hollow fibermembrane 421.

The gas passages 422 (hollow fiber membranes 421) have upper openingswhich open into and communicate with the small space 223. Thus, thesmall space 223 serves as a bubble reservoir that temporarily stores thebubble gas rising from the gas passages 422.

The gas passages 422 also have lower openings which open into andcommunicate with the small space 233 as shown in FIG. 4. The small space233 is in communication with the gas outlet port 29.

With this structure, the bubble gas exiting at the lower openings of thegas passages 422 passes into the small space 233 and then the gas outletport 29 so that is permitted to positively exit out of the oxygenator 1(housing 2). This makes it possible to inhibit or prevent bubbles in theblood passing along the blood passage 33 from going out of the bloodoutlet portion. The gas outlet port 29 can be considered to function asa part of the bubble removal means 4.

The hollow fiber membranes 421 constituting the gas outlet hollow fibermembrane layer 42 and the hollow fiber membranes 31 constituting thehollow fiber membrane bundle 3 may be the same or different in type.

In the case of the hollow fiber membranes 421 and the hollow fibermembranes 31 being different in type, they are preferably different inat least one of material, property and arrangement conditions.

By way of example, the gas outlet hollow fiber membrane layer 42 canpossess a thickness (horizontal length in FIG. 2) of approximately 10-50mm.

The gas outlet hollow fiber membrane layer 42 can also possess a width(vertical length in FIG. 3) of approximately 10-80 mm.

The arrangement pattern, direction, etc. of the hollow fiber membranes421 in the gas outlet hollow fiber membrane layer 42 may be such as toform a structure in which the hollow fiber membranes 421 are arrangedhorizontally, a structure in which the hollow fiber membranes 421 haveobliquely intersecting points (intersections) of one with another, astructure in which all or part of the hollow fiber membranes 421 arearranged in a curved manner, or a structure in which all or part of thehollow fiber membranes 421 are arranged in a corrugated, helical, spiralor annular manner.

With the aspects of the oxygenator described above, a number of effectscan be achieved. For example, gas exchange can be positively made by thehollow fiber membrane bundle 3, with the bubbles in the gas-exchangedblood being positively removed by the gas outlet hollow fiber membranelayer 42. Conditions can be selected for the hollow fiber membranebundle 3 suitable for gas exchange while conditions can be selected forthe hollow fiber membrane layer 42 suitable for gas removal. Therefore,a relatively high performance can be exhibited in both gas exchange andgas removal. Further, the structure having both performances of gasexchange and gas discharge can be received efficiently within the onehousing 2, thus keeping the interval (charge amount) in the bloodpassages 33 relatively small.

The bubbles in the blood containing bubbles that lies upstream of thefilter member 41 (hereinafter, such blood is referred to as“bubble-containing blood”) are adapted to be caught at the filter member41. The blood which has passed the filter member 41 and been subjectedto bubble removal flows toward the blood outlet port 28. By sufficientlyreducing the velocity of the blood entering the passage enlargement 281,the blood moving toward the blood outlet port 28 is prevented fromentraining (against venturi effect), across the filter member 41, thebubbles caught by the filter member 41. This can help assist inpositively preventing the bubbles of the blood from passing out of theblood outlet port 28.

The description which follows describes aspects of the heat exchangingpart (heat exchanger) 1B. The heat exchanger 1B includes the heatexchanger housing 5 which possesses a nearly cylindrical form havingupper and lower closed ends. A blood chamber 50 is formed inside theheat exchanger housing 5. A tubular heating medium inlet port 52 and atubular heating medium outlet port 53 extend from the heat exchangerhousing 5 at the lower end (lower surface) of the heat exchanger housing5. A tubular blood inlet port 51 projects in the lower left region ofthe heat exchanger housing 5 in FIG. 2. The blood inlet port 51 has alumen in communication with the blood chamber 50.

Arranged in the interior of the heat exchanger housing 5 are a heatexchange element 54 that is cylindrical in form, a heating mediumchamber-forming member (cylindrical wall) 55 having a cylindrical formand positioned along the inner periphery of the heat exchange element54, and a partitioning wall 56 separating the inner space of the heatingmedium chamber-forming member 55 into an inlet heating medium chamber 57and an outlet heating medium chamber 58. The heating mediumchamber-forming member 55 serves to form a heating medium chamber thattemporarily stores the heating medium at the inside of the heat exchangeelement 54 and to help prevent the cylindrical heat exchange elementfrom deforming.

The heating medium chamber-forming member 55 and the partitioning wall56 are appropriately fixed in the heat exchanger housing 5, for exampleby bonding through fusion or an adhesive. The heating mediumchamber-forming member 55 and the partitioning wall 56 may be formed asseparate members or may be integrally formed together as a singleunitary one-piece body.

Elongated (strip-formed) openings 59 a, 59 b are formed in the heatingmedium chamber-forming member 55. These openings 59 a, 59 b extendvertically and penetrate through the wall of the heating mediumchamber-forming member 55. The openings 59 a, 59 b are arranged atopposite positions through the partitioning wall 56 as illustrated inFIG. 3. The opening 59 a communicates with the inlet heating mediumchamber 57 while the opening 59 b communicates with the outlet heatingmedium chamber 58.

The heat exchange element 54 can be in the form of a so-calledbellows-type heat exchange element (bellows tube) as shown in FIG. 2.The bellows-type heat exchange element 54 comprises a bellows-formedcentral portion and a cylindrical portion at each end (upper and lowerends). The bellows-formed central portion is comprised of a multiplicityof hollow annular projections that are parallel (inclusive of nearlyparallel) to one another so as to form a plurality of closely arrangedundulations. The inner diameter of each cylindrical end portion is equalto (inclusive of nearly equal to) the inner diameter of thebellows-formed central portion. The heat exchange element 54 can beformed of a metal material such as stainless steel or aluminum, or aresin material such as polyethylene or polycarbonate, for example. It ispreferable to use a metal material, such as stainless steel or aluminumfor reasons of strength and heat exchange efficiency. It is particularlypreferable to use a metal-made bellows tube in a corrugated form havinga multiplicity of repetitive concavo-convex nearly orthogonal to theaxis of the heat exchange element 54.

The heat exchanger housing 5, the heating medium chamber-forming member55 and the partitioning wall 56 can be made of various materials, forexample, polyolefin such as polyethylene or polypropylene, an esterresin (e.g. polyester such as polyethylene terephthalate, orpolybutylene terephthalate), a styrene resin (e.g. polystyrene, MS resinor MBS resin), a resin material such as polycarbonate, various kinds ofceramics materials or a metal material.

With reference to FIGS. 1-3, the following is a description of the flowof heating medium in the heat exchanging part 1B of the oxygenator 1.

The heating medium entering through the heating medium inlet port 52,first flows to the inlet heating medium chamber 57 and then to the outerperipheral side of the heating medium forming member 55 via the opening59 a, thus spreading over the entire periphery of the heating mediumforming member 55 and going into the multiplicity of recesses of thebellows (to the inside of hollow annular projections) of the heatexchange element 54. This heats up or cools down the heat exchangeelement 54 that is in contact with the heating medium. Thus, heatexchange (heating or cooling) is effected with the blood flowing at theouter peripheral side of the heat exchange element 54.

The heating medium serving to heat or cool the heat exchange element 54enters the outlet heating medium chamber 58 through the opening 59 b andthen exits at the heating medium outlet port 53.

Although the oxygenator described above and illustrated in the drawingfigures includes the heat exchanging part 1B, it is to be understoodthat the heat exchanger part 1B is not required, and the oxygenator part1A can be used independently of the heat exchanger part 1B.

Referring to FIGS. 1-4, the following describes the blood flow in theoxygenator 1 of this embodiment.

The blood enters at the blood inlet port 51 and flows into the bloodchamber 50, i.e., between the inner surface of the heat exchangerhousing 5 and the heat exchange element 54, where the blood contacts theouter surface of the plurality of hollow annular projections of the heatexchange element 54, thus effecting heat exchange (heating or cooling).The blood thus subjected to heat exchange gathers at a downstream sideof the blood chamber 50 and then flows into the housing 2 of theoxygenating part 1A through the blood inlet aperture 24.

The blood passing through the blood inlet aperture 24 flows downstreamalong the blood passage 33. Meanwhile, the gas (gas containing oxygen)supplied through the gas inlet port 26 is distributed by the gas inletchamber 261 into the gas passages 32, i.e., the lumens of the hollowfiber membranes 31. After passing along the gas passages 32, the gas iscollected in the gas outlet chamber 271 and allowed to exit at the gasoutlet port 27. The blood, flowing along the blood passage 33 contactsthe outer surfaces of the hollow fiber membranes 31 so that gas exchange(oxygenation or carbon dioxide removal) takes place with the gas flowingthrough the gas passages 32.

If bubbles are present in the gas-exchanged blood, the bubbles arecaught by the filter member 41. The bubbles (bubble gas), caught at thefilter member 41, enter the lumens (gas passages 422) of the hollowfiber membranes 421 via the multiplicity of fine pores in the walls ofthe hollow fiber membranes 421 of the gas outlet hollow fiber membranelayer 42 located adjacent to and upstream of the filter member 41. Thebubble gas entering the hollow fiber membranes 421 is discharged at thegas outlet port 29 through the small space 233.

The blood thus subjected to gas exchange and bubble removal flows out ofthe blood outlet port 28.

In the oxygenator 1 of this embodiment, it is preferable that surfacesto be contacted with blood (e.g., the inner surface of the housing 2,the inner surface of the heat exchanger housing 5, the surface of theheating medium chamber-forming member 55, the surface of thepartitioning wall 56, the setting member 7, and the surfaces of thepartitioning walls 8, 9 facing the blood passage 33) are madeantithrombotic. The antithrombotic surface can be formed by coating andfixing an antithrombotic material on the surface. Examples of theantithrombotic material include heparin, urokinase, HEMA-St-HEMAcopolymer, poly-HEMA and so on.

The flow rate of blood through the blood inlet port 51 is not especiallylimited because it may be different depending upon, for example, thepatient's physique and the operational scheme. However, usually, a bloodflow rate of 0.1-2.0 L/min is preferred in the case of an infant orchild, a blood flow rate of 2.0-5.0 L/min is preferred in the case of achild in elementary or middle school, and a blood flow rate of 3.0-7.0L/min is preferred in the case of an adult.

The flow rate of the gas supplied through the gas inlet port 26 is alsonot particularly limited because it is different depending upon, forexample, the patient's physique and the operational scheme. However,usually, a gas flow rate of 0.05-4.0 L/min is preferred in the case ofan infant or child, a gas flow rate of 1.0-10.0 L/min is preferred inthe case of a child in elementary or middle school, and a gas flow rateof 1.5-14.0 L/min is preferred in the case of an adult.

Similarly, the oxygen concentration of the gas supplied through the gasinlet port 26 is not especially limited because it may differ dependingupon, for example, the metabolic amount of oxygen/carbon-dioxide gas ofa patient under operation. However, an oxygen concentration of 40-100%can be used.

The maximum continuous operation time of the oxygenator 1 can varydepending upon the patient's condition and the operational scheme.However, a time of approximately 2-6 hours can be considered. Themaximum continuous operation time of the oxygenator 1 may, rarely,amount to a time as long as nearly 10 hours.

FIG. 5 illustrates a second embodiment of the oxygenator. Thedescription which follows primarily describes the differences betweenthis embodiment and the foregoing embodiment described above. Thus,features of the oxygenator which are similar to those in the firstembodiment are identified by the same reference numerals and a detaileddescription of such features is not repeated. This second embodiment issimilar to the first embodiment, except for features relating to thehousing.

In the oxygenator 1′ shown in FIG. 5, the rectangular cylindricalhousing body 21 (housing 2) has, at its downstream side, a wall (sidewall) 211 inclined relative to the axis of the rectangular cylindricalhousing body 21 (i.e., relative to the vertical). Thus, in theoxygenator 1′, the rectangular cylindrical housing body 21 has across-sectional area gradually increasing toward the lower portion(toward a passage enlargement 281) in FIG. 5. Accordingly, between theinner surface (wall 211) of the rectangular cylindrical housing body 21and the filter member 41, a gap is provided (i.e., a gap having a sizeor width t of a blood outlet aperture 25) that gradually increasestoward the passage enlargement 281 (toward the downstream end).

By gradually increasing the gap size t, the blood moving down the bloodoutlet aperture 25 is decelerated until reaching the passage enlargement281. By moderately decelerating the flow velocity, the blood is allowedto flow in a manner that does not significantly adversely affect asmooth flow, thus providing a flow-velocity distribution through theblood passage 33 with a result that the pressure loss of blood flow canbe held relatively low.

Although FIG. 5 illustrates the gap size as increasing continuously andgradually, the wall 211 can be configured to provide a gap size t thatincreases stepwise toward the downstream end (i.e., toward the lowerend).

The (lower) region of the blood outlet aperture 25 increasing in gapsize t is due to an increasing cross-sectional area of the blood outletaperture 25A, and hence is capable of exhibiting a function similar tothat of an enlargement (e.g., the enlargement 282A in a furtherembodiment described below).

FIGS. 6-11 illustrate a third embodiment of an oxygenator describedherein. In FIGS. 6, 8 and 9, the left side is referred to as “left” or“leftward” while the right side is referred to as “right” or“rightward”. In FIGS. 6-8, 10 and 11, the upper side is referred to as“upper” or “above” while the lower side is referred to as “lower” or“below”. In FIGS. 6-11, the interior of the oxygenator is referred to asthe “blood inlet side” or “upstream side” while the exterior thereof isreferred to as “blood outlet side” or “downstream side”.

The description which follows primarily describes the differencesbetween this embodiment and the foregoing embodiments described above.Thus, features of the oxygenator which are similar to those previouslydescribed in other embodiments are identified by the same referencenumerals and a detailed description of such features is not repeated.

This third embodiment is similar to the first embodiment except that theoxygenator is different in its overall shape. The oxygenator 10 in theillustrated embodiment possesses a nearly cylindrical form in its entireor overall shape (exterior shape). The oxygenator 10 is a heatexchanger-equipped oxygenator including a heat exchanging part (heatexchanger) 10B provided in the interior thereof which is nearly similarin structure to the heat exchanging part 1B of the first embodiment, andan oxygenating part 10A provided at an outer periphery of the heatexchanging part 10B for performing gas exchange with respect to theblood.

The oxygenator 10 comprises a housing 2A in which is received orpositioned the oxygenating part 10A and the heat exchanging part 10B. Asshown in FIG. 10, the oxygenating part 10A and the heat exchanging part10B are arranged concentric to the housing 2A.

The heat exchanging part 10B is further received in a heat exchangerhousing 5A within the housing 2A. By virtue of the heat exchangerhousing 5A, both ends of the heat exchanging part 10B are fixed relativeto the housing 2A.

The housing 2A is comprise of a housing body 21A possessing acylindrical form (hereinafter referred to as a “cylindrical housingbody”), a first header (upper lid) 22A in a dish form closing theleft-side aperture or opening of the cylindrical housing body (barrel)21A, and a second header (lower lid) 23A in a dish form closing theright-side aperture or opening of the cylindrical housing body 21A.

The cylindrical housing body 21A, the first header 22A and the secondheader 23A are each formed of, for example, polyolefin such aspolyethylene or polypropylene, an ester resin (e.g. polyester such aspolyethylene terephthalate, or polybutylene terephthalate), a styreneresin (e.g. polystyrene, MS resin or MBS resin), a resin material suchas polycarbonate, a ceramics material in various kind or a metalmaterial. The first header 22A and the second header 23A are secured ina liquid-tight manner to the cylindrical housing body 21A by joining,for example by fusion or an adhesive.

A tubular blood outlet port 28 is formed in the outer periphery of thecylindrical housing body 21A. The blood outlet port 28 projects nearlyin a tangential direction to the outer peripheral surface(circumference) of the cylindrical housing body 21A as shown in FIGS. 7and 10. In the construction shown in FIG. 10, the portion of the bloodoutlet port 28 which opens to the housing body 21A is offset outwardlyaway from the inner peripheral surface of the cylindrical housing body21A (an imaginary continuation of the inner peripheral surface) by adistance C to thus provide a passage enlargement as described in moredetail below. By way of example, the distance or offset C can preferablybe approximately 0.5-4 mm.

A blood outlet aperture 25A, described in more detail below, is in acylindrical form concentric to the cylindrical housing body 21A. Theblood outlet port 28 thus projects nearly tangentially to thecircumference of the blood outlet aperture 25A. This allows the bloodpass along the blood outlet aperture 25A to flow into the blood outletport 28 relatively smoothly and easily.

A passage enlargement 281, possessing a box form (or a groove form), isprovided in a region nearby the blood outlet port 28 and close to thecylindrical housing body 21A or housing 2 (at and around the upstreamend), i.e., in a base region of the blood outlet port 28. The bloodoutlet port 28 has a lumen in communication with a lumen of the passageenlargement 281, thus forming a passage through which the blood passingthrough a filter member 41A, described in more detail below, is to pass.As shown in FIGS. 8 and 10, the passage enlargement 281 is provided as aregion where the passage is increased in its cross-sectional area.

In the oxygenator 1, the blood passing through the filter member 41A,upon entering the passage enlargement 281, is decelerated at a ratereciprocal to the increasing ratio of the passage cross-sectional area.The blood whose velocity has been decelerated reaches the blood outletport 28.

A blood inlet port 201 and a gas outlet port 27 that are tubular in formproject from the first header 22A. The blood inlet port 201 is formed inan end surface of the first header 22A such that the axis of the bloodinlet port 201 is offset from the center of the first header 22A asshown in FIG. 7. The gas outlet port 27 is formed in the outer peripheryof the first header 22A such that the axis of the gas outlet port 27intersects the center of the first header 22A as shown in FIG. 7.

A gas inlet port 26, a gas outlet port 29, a heating medium inlet port202 and a heating medium outlet port 203 that are tubular in formproject from the second header 23A. The gas inlet port 26 and the gasoutlet port 29 are formed in the end-surface of the second header 23A atan edge of the second header 23A. The heating medium inlet port 202 andthe heating medium outlet port 203 are formed nearly centrally in theend surface of the second header 23A. The heating medium inlet port 202and the heating medium outlet port 203 are somewhat inclined so thattheir axes form an angle relative to the centerline of the second header23A.

The oxygenating part 10A is concentrically arranged or received in theinterior of the housing 2A. The oxygenating part 10A is cylindrical inform and extends along the inner peripheral surface of the housing 2A asshown in FIGS. 8-10. The oxygenator 10A is comprised of a hollow fibermembrane bundle 3A in a cylindrical form, a filter member 41A serving asbubble removal means 4A provided on the outer peripheral side (bloodoutlet side) of the hollow fiber membrane bundle 3A, and gas outlethollow fiber membrane layer 42A. The hollow fiber membrane bundle 3A,the gas outlet hollow fiber membrane layer 42A and the filter member 41Aare arranged in that order, with the hollow fiber membrane bundle 3Abeing located innermost relative to the gas outlet hollow fiber membranelayer 42A and the filter member 41A.

As shown in FIG. 11, the hollow fiber membrane bundle 3A is formed byintegrating a multiplicity of hollow fiber membranes 31 serving for gasexchange.

The arrangement pattern, direction, etc. of the hollow fiber membranes31 of the hollow fiber membrane bundle 3A can be arranged verticalrelative to the axis of the housing 2A, or can be arranged to form astructure in which the hollow fiber membranes 31 have obliquelyintersecting points (intersections) with another (intersections), astructure in which all or part of the hollow fiber membranes 31 arearranged curved, or a structure in which all or part of the hollow fibermembranes 31 are arranged in a corrugated, helical, spiral or annularmanner.

The hollow fiber membranes 31 at their opposite ends (left and rightends) are fixed to the inner surfaces of the rectangular cylindricalhousing body 21A by partitioning walls 8, 9 as shown in FIGS. 9 and 10.

The hollow fiber membrane bundle 3A is charged nearly fully between thecylindrical housing body 21A and the heat exchanger part 10B. Due tothis, the hollow fiber membrane bundle 3A is wholly placed nearly in acylindrical form. This provides a relatively high charge efficiency ofthe hollow fiber membranes 31 (with less dead space) in the cylindricalhousing body 21A, thus contributing to a size reduction and performanceimprovement of the oxygenating part 10A.

The hollow fiber membranes 31, between the partitioning walls 8, 9 inthe housing 2A, are exposed so that a blood passage 33 is formed outsidethe hollow fiber membranes 31, i.e., at the gaps between the hollowfiber membranes 31, allowing blood to flow from left to right in FIG. 2.The same is true for the hollow fiber membranes 421 of the gas outletfiber membrane layer 42A.

A cylindrical blood inlet aperture (blood inlet space) 24A is formed asa blood inlet portion for the blood entering from the blood inlet port201 upstream of the blood passage 33 (closer to the upstream surface ofthe hollow fiber membrane bundle 3A), i.e., between the oxygenator part10A and the heat exchanging part 10B.

The blood entering the blood inlet aperture 24A flows in a directionperipheral of and lengthwise of the blood inlet aperture 24A and is thusallowed to flow to the entirety of the blood inlet aperture 24A. Thismakes it possible to efficiently transfer the blood from the heatexchanging part 10B to the oxygenating part 10A.

Downstream of the blood passage 33 (closer to the downstream surface ofthe hollow fiber membrane bundle 3A), a cylindrical gap is formedbetween the outer peripheral surface of the filter member 41A and theinner peripheral surface of the cylindrical housing body 21A. The gap islocated where the blood which has passed through the filter member 41Ais to flow, thus forming a blood outlet aperture (blood outlet space)25A. A blood outlet portion is constituted by the blood exit aperture25A, the passage enlargement 281 and the blood outlet port 28communicating with the blood outlet aperture 25A through the passageenlargement 281. The blood outlet aperture 25A has a gap size t that isconstant and extends circumferentially of the blood outlet aperture 25A.

The blood outlet aperture 25A thus arranged provides the blood exitportion with a space where the blood which has passed through the filtermember 41A is to flow toward the blood outlet port 28. Thus, the bloodcan be discharged smoothly.

Between the blood inlet aperture 24A and the blood outlet aperture 25A,there exist the hollow fiber membrane bundle 3A, the filter member 41A,the gas outlet hollow fiber membrane layer 42A and the blood passage 33.

The thickness of the hollow fiber membrane bundle 3A (i.e., the radiallength in FIG. 10) is not particularly limited, but is preferablyapproximately 2-100 mm, more preferably approximately 3-30 mm.

As mentioned before, the bubble removal means 4A is positioneddownstream (closer to the blood exit portion) of the hollow fibermembrane bundle 3A, serving to catch bubbles in the blood and dischargethe caught bubbles to the outside of the blood passage. The bubbleremoval means 4A comprises the filter member 41A and the gas outlethollow fiber membrane layer 42A arranged upstream of the filter member41A.

The filter member 41A is formed by a sheet member that is nearlyrectangular in form (hereinafter also referred to as a “sheet”), whereinthe sheet is wound in a cylindrical form. The filter member 41A has bothends respectively secured by the partitioning walls 8, 9 so that thefilter member 41A is fixed in the housing 2A as shown in FIGS. 8 and 9.

The inner peripheral surface of the filter member 41A contacts thedownstream surface (closer to the blood outlet portion) of the gasoutlet hollow fiber membrane layer 42A. In the illustrated embodiment,the filter member 41A contacts and covers the entire outer surface ofthe gas outlet hollow fiber membrane layer 42A (inclusive ofsubstantially the entire outer surface of the gas outlet hollow fibermembrane layer 42A). By thus providing the filter member 41A, the filtermember 41A can be increased in effective area thus relatively fullyexhibiting the capability of catching bubbles. By increasing theeffective area of the filter member 41A, even if clogging occurs in apart of the filter member 41A (e.g., adhesion of blood aggregations), itis possible to suppress or prevent the possibility that blood flowthrough the filter member 41A will be entirely blocked.

The filter member 41A can be in a form similar to the filter member ofthe first embodiment, i.e., a mesh (meshwork) form, a woven fabric, anon-woven fabric or a combination thereof. Also, the material formingthe filter member 41A can be similar to that of the filter member 41 ofthe first embodiment.

By arranging the filter member 41A thus structured, even if bobblesexist in the blood flowing along the blood passage 33, the bubbles canbe caught to prevent bubbles from passing out of the blood outlet port28.

The bubbles caught by the filter member 41A are removed by the gasoutlet hollow fiber membrane layer 42A located upstream of the filtermember 41A.

It is to be understood that the gas outlet hollow fiber membrane layer42A described above is not essential and can be omitted, if desired. Inembodiments where the gas outlet hollow fiber membrane layer 42A is notutilized, bubbles trapped by the filter member 41A are removed by thehollow fiber membranes 31.

That is, in the case that bubbles exist in the gas-exchanged blood, suchbubbles are caught by the filter member 41A. The bubbles (bubble gas),caught at the filter member 41A pass through the multiplicity of finepores of the hollow fiber membranes 31 of the hollow fiber membranebundle 3 located upstream of the filter member 41A, and then enter thelumens of the hollow fiber membranes 31 (gas passages 32). The bubblegas entering the hollow fiber membranes 31 is discharged at the gasoutlet port 27 through the gas outlet chamber 271.

As shown in FIG. 11, almost all of the hollow fiber membranes 421forming the gas outlet hollow fiber membrane layer 42A are arrangednearly parallel with the hollow fiber membranes 31 forming the hollowfiber membrane bundle 3A. Both ends (i.e., the upper and lower ends) ofthe hollow fiber membranes 421 are respectively fixed to the innersurfaces of the cylindrical housing body 21A through the partitioningwalls 8, 9 in a manner similar to the hollow fiber membranes 31 as shownin FIGS. 8 and 9.

The arrangement pattern, direction, etc. of the hollow fiber membranes421 in the gas outlet hollow fiber membrane layer 42A are not limited tothose mentioned as the gas outlet hollow fiber membrane layer 42A can bearranged as a structure in which the hollow fiber membranes 421 arearranged vertical to the axis of the housing 2A, a structure in whichthe hollow fiber membranes 421 have obliquely intersecting points(intersections) of one with another, a structure in which all or part ofthe hollow fiber membranes 421 are arranged curved, or a structure inwhich all or part of the hollow fiber membranes 421 are arranged in acorrugated, helical, spiral or annular manner.

The thickness of the gas outlet hollow fiber membrane layer 42A (i.e.,the radial length in FIG. 10) is not particularly limited, but ispreferably, approximately 1-50 mm, more preferably approximately 1-30mm.

As shown in FIG. 9, a first chamber 221 a is defined by the first header22A, the partition wall 8, the heat exchanger housing 5A of the heatexchanging part 10B, and the heating medium chamber-forming member 55.The first chamber 221 a is divided by a partition 222 into a gas outletchamber 271 located close to the hollow fiber membrane bundle 3A and asmall space 223 located close to the gas outlet hollow fiber membranelayer 42A. The partition 222 is located at the boundary between thehollow fiber membrane bundle 3A and the gas outlet hollow fiber membranelayer 42A. The hollow fiber membranes 31 have left-end openings openinginto and communicating with the gas outlet chamber 271.

In addition, a second chamber 231 a is defined by the second header 23A,the partition wall 9, the heat exchanger housing 5A of the heatexchanging part 10B, and the heating medium chamber-forming member 55.The second chamber 231 a is divided by a partition 232 into a gas inletchamber 261 located closer to the hollow fiber membrane bundle 3A and asmall space 233 located closer to the gas outlet hollow fiber membranelayer 42A. The partition 232 is located at the boundary between thehollow fiber membrane bundle 3A and the gas outlet hollow fiber membranelayer 42A. The hollow fiber membranes 31 have right-end openings thatopen into and communicate with the gas inlet chamber 261 as shown inFIG. 11.

The hollow fiber membranes 31 each have a lumen forming a gas passage 32through which gas is adapted to flow. The gas inlet port 26 and the gasinlet chamber 261 constitute a gas inlet located upstream of the gaspassages 32, while the gas outlet port 27 and the gas outlet chamber 271constitute a gas outlet portion located downstream of the gas passages32.

The hollow fiber membranes 421 each have lumen forming a gas passage 422through which the bubble gas, passing through a multiplicity of finepores formed in the wall of the hollow fiber membrane 421, is adapted toflow.

The gas passages 422 (hollow fiber membranes 421) have left-end openingsthat open into and communicate with the small space 223. This allows thesmall space 223 to serve as a bubble reservoir for temporarily storingthe bubble gas flowing out of the gas passages 422.

The gas passages 422 also have right-end openings that open into andcommunicate with the small space 233 as shown in FIG. 11. The smallspace 233 communicates with the gas outlet port 29.

With this structure, the bubble gas passing out of the right-endopenings of the gas passages 422 enters the small space 233 and then thegas outlet port 29, thus being positively discharged out of theoxygenator 10 (housing 2A). This can positively prevent the bubbles inthe blood flowing along the blood passage 33 from being discharged outof the blood outlet.

The bubbles in the bubble-containing blood located upstream of thefilter member 41A are caught by the filter member 41A. The blood passingthrough the filter member 41A and subjected to bubble removal flowstoward the blood outlet port 28. By sufficiently decreasing the velocityof the blood entering the passage enlargement 281, the blood movingtoward the blood outlet port 28 is prevented from entraining (againstthe venturi effect), across the filter member 41A, the bubbles that arecaught by the filter member 41A. This can positively prevent the bubblesof the blood from being discharged out of the blood outlet port 28.

As mentioned before, the oxygenating part 10A is arranged in the heatexchanging part 10B. The heat exchanging part 10B is similar inconstruction to the heat exchanging part 1B described above and so adetailed description is not repeated.

By thus arranging the heat exchanging part 10B in the oxygenating part10A, a number of advantages can be realized. For example, theoxygenating part 10A and the heat exchanging part 10B are efficientlyreceived in the same housing 2A and so there is less dead space. Gasexchange can thus be achieved efficiently by the relatively small-sizedoxygenator 10. Additionally, because the oxygenating part 10A and theheat exchanging part 10B are placed in a closer arrangement than thosein the first embodiment, the blood heat exchanged at the heat exchangingpart 10B is allowed to flow rapidly into the oxygenator 10A. This canminimize the charge amount of blood in the blood inlet aperture 24A(blood passage 33) communicating between the heat exchanging part 10Band the oxygenator 10A. Further, the blood subjected top heat exchangeat the heat exchanging part 10B can flow to the oxygenating part 10Arapidly without significant delay.

Referring to FIGS. 8-11, the following is a description of the bloodflow in the oxygenator 10 of this embodiment.

In the oxygenator 10, the blood enters at the blood inlet port 201 andflows to the blood chamber 50, i.e., to between the inner peripheralsurface of the heat exchanger housing 5A and the heat exchange element54. The blood contacts the outer surface of the plurality of hollowannular projections forming the heat exchange element 54 to thus effectheat exchange (heating or cooling). The blood thus heat exchanged passesthrough an opening 59 c formed in the upper portion of the heatexchanger housing 5A and the blood inlet opening 24A in that order, andthen flows into the housing 2A of the oxygenator 10A.

The blood, passing through the blood inlet opening 24A flows downstreamalong the blood passage 33. Meanwhile, the gas supplied through the gasinlet port 26 (gas containing oxygen) is distributed from the gas inletchamber 261 into the gas passages 32, i.e., into the lumens of thehollow fiber membranes 31. After flowing along the gas passages 32, thegas is collected in the gas outlet chamber 271 and is discharged at thegas outlet port 27. The blood flowing along the blood passage 33contacts the outer surface of the hollow fiber membranes 31 where it isgas-exchanged (oxygenated, carbon dioxide removal) with the gas flowingthrough the gas passages 32.

If bubbles exist in the gas-exchanged blood, such bubbles are caught bythe filter member 41A. The bubbles (bubble gas) caught at the filtermember 41A pass through a multiplicity of fine pores of the hollow fibermembranes 421 of the gas outlet hollow fiber membrane layer 42A locatedadjacent and upstream of the filter member 41A, and then enters thelumens of the hollow fiber membranes 421 (gas passages 422). The bubblegas entering the hollow fiber membranes 421 is discharged at the gasoutlet port 29 through the small space 233.

The blood, thus gas-exchanged and subjected to bubble removal, isallowed to exit at the blood outlet port 28.

FIG. 12 illustrates a fourth embodiment of an oxygenator disclosedherein. The description which follows primarily describes thedifferences between this embodiment and the foregoing embodimentsdescribed above. Thus, features of the oxygenator which are similar tothose previously described in other embodiments are identified by thesame reference numerals and a detailed description of such features isnot repeated.

The present embodiment is similar to the third embodiment describedabove, except that an oxygenating part is received or positionedeccentrically in the housing.

In the oxygenator 10′ shown in FIG. 12, the oxygenator part 10A isarranged eccentric upward relative to the housing 2A (cylindricalhousing body 21A). A gap exists between the inner peripheral surface ofthe cylindrical housing body 21A and the outer peripheral surface of thefilter member 41A. This gap possesses a size (width dimension) t in theblood outlet aperture 25A, gradually increasing toward the downstreamend along the periphery, i.e., toward the passage enlargement 281. Thus,in the blood outlet aperture 25A, the gap size t is a minimum sizet_(min) at its upper region (diametrically opposite to the passageenlargement 281) and is a maximum size t_(max) at its lower region ordownstream portion (i.e., at the passage enlargement 281).

Thus, the blood outlet aperture 25A, in a portion nearby the maximum gapt_(max), is enlarged in its passage cross-sectional area, correspondingto a first enlargement 282A of a seventh embodiment described in moredetail below, thus exhibiting a function similar to that of the firstenlargement 282A.

By thus gradually increasing the gap size t, the blood passing throughthe blood outlet aperture 25A is further decelerated until reaching thepassage enlargement 281. Owing to the moderate decrease of velocity, theblood is allowed to flow in a manner that does not significantlyadversely affect a smooth flow, wherein the distribution of flowvelocity is relatively uniform along the blood passage 33, with a resultthat the pressure loss due to blood flow can be suppressed.

FIG. 13 illustrates a fifth embodiment of an oxygenator. The followingdescription primarily describes the differences between this embodimentand the first embodiment described above. Thus, features of theoxygenator which are similar to those previously described areidentified by the same reference numerals and a detailed description ofsuch features is not repeated.

The oxygenator 1 of this embodiment is similar to that of the firstembodiment except that the gas outlet hollow fiber membrane layer 42 andthe gas outlet port 29 are not present. That is, the bubble removalmeans 4 in this embodiment is comprised of the filter member 41. Inaddition, no partitions 222, 232 are provided because of the absence ofthe gas outlet port 29.

FIG. 14 depicts a sixth embodiment of the oxygenator. The descriptionwhich follows primarily describes the differences between thisembodiment and the second embodiment described above. Thus, features ofthe oxygenator which are similar to those previously described areidentified by the same reference numerals and a detailed description ofsuch features is not repeated.

The oxygenator 1′ according to this embodiment is similar to that of thesecond embodiment described above, except that the gas outlet hollowfiber membrane layer 42 and the gas outlet port 29 are not present. Thatis, the bubble removal means 4 used in this embodiment is comprised ofthe filter member 41. Also, no partitions 222, 232 are provided due tothe absence of the gas outlet port 29.

FIGS. 15 and 16 illustrate a seventh embodiment of an oxygenatoraccording to the invention. The following description primarilydescribes differences between this embodiment and the third embodimentdescribed above. Thus, features of the oxygenator which are similar tothose previously described are identified by the same reference numeralsand a detailed description of such features is not repeated.

The oxygenator 10″ of this embodiment is similar to that of the thirdembodiment shown in FIGS. 6-11, except that the gas outlet hollow fibermembrane layer 42, the gas outlet port 29 and the partitions 222, 232are not present. In addition, the passage enlargement is different instructure.

The bubble removal means 4 in this embodiment is comprised of the filtermember 41. As noted, the gas outlet hollow fiber membrane layer 42 andthe gas outlet port 29 are not included. Also, no partitions 222, 232are provided because of the nonexistence of a gas outlet port 29. Thefilter member 41 should preferably closely contact the hollow fibermembrane bundle 3A.

In this embodiment, a passage enlargement 282 is formed by a firstenlargement 282A provided on an upstream side and a second enlargement282B following the first enlargement 282A at a downstream side. Thisarrangement can help further prevent bubble from exiting out of theblood outlet port 28.

In the vicinity of the base of a blood outlet port 28, a groove (groovedrecess) is formed axially along the inner peripheral surface of acylindrical housing body 21A as best shown in FIG. 16. In theillustrated embodiment, the groove has a constant width. The grooveconstitutes the first enlargement 282A. In other words, the firstenlargement 282A is provided as a portion of the cylindrical housingbody 21A where the inner diameter of the housing body 21A is partially(locally) enlarged. The reason that the enlarged portion is preferablyarranged along only a portion of the inner surface of the housing body21A is to restrain increasing the priming volume while still reducingthe blood current speed.

The groove, constituting the first enlargement 282A, is preferablyformed throughout the axial (longitudinal) length of the cylindricalhousing body 21A, i.e., over the entire axial extent of a blood outletaperture 25A as shown in FIG. 16. This is because the blood can bedecelerated uniformly and positively at axial points in the blood outletaperture 25A.

By virtue of the first enlargement 282A structured in this way, theblood outlet aperture 25A has an increased gap size. That is, ascompared to the first enlargement 282A not being present so that the gapsize is represented by t, the gap size t1 (corresponding to t_(max) ofthe fourth embodiment) where the first enlargement 282A is formed isgreater than the foregoing gap size t. It is preferable that therelationship of t1/t is approximately 1.05-12, more preferablyapproximately 1.05-10. The relationship t1-t is preferably approximately0.05-20 mm, more preferably approximately 0.1-10 mm.

When t1/t or t1-t is in the ranges mentioned above, a proper bloodvelocity decrease can be achieved by first enlargement 282A, thuscontributing to improving the effect of preventing bubbles from exitingout of the blood outlet port 28.

The width (groove width) of the first enlargement 282A is notparticularly limited. However, the first enlargement 282A has a width orchord length W (shown in FIG. 16) in its formed region as viewedlaterally from the side where the blood outlet port 28 of thecylindrical housing body 21A is formed (i.e., as viewed from below inFIG. 15 and as viewed from the front in FIG. 16) that is preferablyapproximately 35-99% of the inner diameter of the cylindrical housingbody 21A, more preferably approximately 45-75%. When the width W iswithin such numerical ranges, blood velocity decrease can be properlymade by the first enlargement 282A, thus contributing to the effect ofpreventing bubble from exiting out of the blood outlet port 28.

The second enlargement 282B is similar to the passage enlargement 28(passage enlargement 28 formed in the base of the blood outlet port 28)of the third embodiment.

In the oxygenator 10″ of this embodiment, the blood passes the throughthe hollow fiber bundle 3A and the filter member 41A in that order andthen enters the blood outlet aperture 25A. The blood flows in the bloodoutlet aperture 25A along its periphery and toward the first enlargement282A, and flows into the first enlargement 282A where the blood passageincreases its width from t to t1. Thus, the blood is decreased in flowvelocity. The blood, entering the first enlargement 282A flows along thefirst enlargement 282A toward the lengthwise center thereof (toward thesecond enlargement 282B), and flows into the second enlargement 282B.Here again, the blood is decelerated. Then, the blood flows to the bloodoutlet port 28 and to the outside of the housing 2A.

The bubbles trapped by the filter member 41 enter into the inside lumenof the hollow fiber membranes of the hollow fiber membrane bundle 3Athrough the multiplicity of pores formed in the hollow fiber membraneslocated close to the filter member 41. The other embodiments (e.g., thefifth and sixth embodiments described above, and the eighth and ninthembodiments described below) have the same bubble removal mechanism asthis seventh embodiment.

FIG. 17 illustrates an eighth embodiment of an oxygenator. Thedescription which follows primarily describes the differences betweenthis embodiment and the third embodiment described above. Thus, featuresof the oxygenator which have already been described are identified bythe same reference numerals and a detailed description of such featuresis not repeated.

The oxygenator 1 of this embodiment is similar to that of the thirdembodiment, except that the gas outlet hollow fiber membrane layer 42Aand the gas outlet port 29 are not present. That is, a filter member 41Ais provided by contacting its inner peripheral surface with thedownstream surface of the hollow fiber membrane bundle 3A (closer to theblood outlet). In this embodiment, the bubble removal means 4A iscomprised of the filter member 41A.

In addition, this embodiment does not include the partitions 222, 232because of the absence of the gas outlet port 29.

FIG. 18 depicts a ninth embodiment of an oxygenator. The descriptionwhich follows primarily describes the differences between thisembodiment and the fourth embodiment described above. Thus, features ofthe oxygenator which have already been described are identified by thesame reference numerals and a detailed description of such features isnot repeated.

The oxygenator 10 in this embodiment is similar to that of the fourthembodiment, except that the gas outlet hollow fiber membrane layer 42Aand the gas outlet port 29 are not present. Namely, a filter member 41Ais provided by contacting its inner peripheral surface with the outersurface of a hollow fiber membrane bundle 3A, including the downstreamsurface of the hollow fiber membrane bundle 3A (closer to the bloodoutlet portion). In this embodiment, the bubble removal means 4A iscomprised of the filter member 41A.

This embodiment does not include the partitions 222, 232 because of theabsence of the gas outlet port 29.

FIG. 19 is an illustration of a tenth embodiment of an oxygenator asdisclosed herein. The description which follows primarily describes thedifferences between this embodiment and the seventh embodiment describedabove. Thus, features of the oxygenator which have already beendescribed are identified by the same reference numerals and a detaileddescription of such features is not repeated.

The oxygenator 100 in this embodiment is similar to that of the seventhembodiment, except that instead of including both a first enlargementand a second enlargement as in the seventh embodiment, this tenthembodiment includes only the first enlargement.

The oxygenator has been described by way of the illustrated embodiments.However, the invention is not limited to such embodiments becausevarious elements constituting the oxygenator can be replaced withfeatures or elements capable of exhibiting the same or similarequivalent functions.

For example, different structures from those illustrated and describedare appropriate for the structure or form of the housing, including theheat exchanger housing, and the position and projecting direction of thegas inlet port, gas outlet port, blood outlet port, blood inlet port,heating medium inlet port, heating medium outlet port, etc. The positionof the oxygenator in use (positional relationship of various elementsrelative to the vertical direction) is also not limited to theillustrated position.

Below is a description of concrete examples of the oxygenator disclosedherein.

Example 1

Three types (models 1, 2 and 3) of oxygenators were fabricated accordingto the seventh embodiment shown in FIGS. 15 and 16, but differing fromone another in the size of the cylindrical housing body (outer shell)and hollow fiber membrane bundle. The constructions are detailed inTable 1. The oxygenator has an outer shell formed with a secondenlargement as a passage enlargement in a base of the blood outlet portas shown in FIG. 15, and a first enlargement in a groove form extendinglengthwise of the outer shell in the vicinity of the second enlargementin the inner peripheral surface of the outer shell as shown in FIG. 16.The hollow fiber membranes used are those used in Capiox® RX25, RX15 andRX05 marketed by Terumo Kabushiki Kaisha. The hollow fiber membranes arewound around the core like the Capiox RX25, RX15 and RX05.

The filter member is made of a hydrophilic sheet-formed mesh ofpolyester and having a thickness of 70 μm and a mesh size of 40 um.

Example 2

A fourth model (model 4) of oxygenator was fabricated according to theconstruction shown in FIG. 19 (tenth embodiment). The construction isdetailed in Table 1 below. The oxygenator has the first enlargement in abase of the blood outlet port as shown in FIG. 19. The hollow fibermembranes forming the hollow fiber membrane bundle and the filter memberare similar to those of Example 1.

Comparative Example 1

As comparative examples, the oxygenators used were Capiox® RX25 (model5), RX15 (model 6) and RX05 (model 7) marketed by Terumo KabushikiKaisha. A gas outlet fiber membrane layer and a filter member areabsent. As shown in FIG. 20, the outer shell has an inner peripheralsurface having a tangential line coincident with the inner surface ofthe blood outlet port. That is, in these Comparative Examples, a passageenlargement (second passage enlargement) is not existent. A firstpassage enlargement also is absent. The construction of theseComparative Examples is detailed in Table 1.

Comparative Example 2

Another oxygenator (model 8) similar to that of Comparative Example 1was fabricated, except that a filter member the same in type as used inExample 1 was provided in the outer peripheral surface of the hollowfiber membrane bundle. The oxygenator of Comparative Example 2 (model 5)has the conditions or characteristics shown in Table 1.

TABLE 1 Oxygenator Specification Comparative Example 1 ComparativeExample 1 Example 2 Model 5 Model 6 Model 7 Example 2 Model 1 Model 2Model 3 Model 4 RX25 RX15 RX05 Model 8 Inner diameter of oxygenatorouter shell 108 107.5 75.56 108 108 107.5 75.56 108 d[mm] Outermostdiameter of hollow fiber 105 105 73.8 105 105 105 73.8 105 membranebundle D[mm] Effective length of hollow fiber membrane 90 52 28 90 90 5228 90 L[mm] Presence/absence of filter member Present Present PresentPresent Absent Absent Absent Present Presence/absence of passageenlargement Present/ Present/ Present/ Present/ Absent/ Absent/ Absent/Absent/ (first enlargement/second enlargement) present present presentabsent absent absent absent absent Gap size between filter member (orhollow 1.5 1.25 0.88 1.5 1.5 1.25 0.88 1.5 fiber membrane bundle) andouter shell inner peripheral surface t [mm] the first enlargement t1[mm] 2.75 2.75 1.88 2.75 1.5 1.25 0.88 1.5 the second enlargement c [mm]1 1 1 0 0 0 0 0 Passage area of the first enlargement 2.48 1.43 0.532.48 1.35 0.65 0.25 1.35 (S = t1 × L) [cm²] Total flow rate of bloodQ(=Q1 + Q2)[mL/min] 7000 5000 1500 7000 7000 5000 1500 7000 Flow rate ofblood through clearance 3500 2500 750 3500 3500 2500 750 3500(semicircular) Q1 (=Q2)[mL/min] Mean blood velocity (=Q1 ÷ S)[cm/min]1414 1748 1425 1414 2593 3846 3044 2593 Mesh size of Filter member [μm]40 40 40 40 — — — 40 Distance between filter member (or hollow 3.75 3.752.88 2.75 1.5 1.25 0.88 1.5 fiber membrane bundle) and blood outlet portt2 [mm] Condition of the first enlargement Gap size increment Δt(=t1 −t) [mm] 1.25 1.5 1 1.25 — — — — First enlargement width (chord length)66 66 37.5 66 — — — — W [mm] First enlargement depth (lengthlongitudinal 90 52 28 90 — — — — of outer shell) [mm]

Bubble Removal Performance Test

The following bubble removal performance test was conducted on theoxygenators (models 1-8) of Examples 1 and 2, and Comparative Examples 1and 2.

The oxygenators of models 1-8 were each incorporated into a bloodextracorporeal circulation circuit to circulate the blood of a testanimal (cattle blood, hematocrit value=35%, blood temperature=37° C.) ata flow rate shown in Table 3. In a position immediately preceding theblood inlet port of the oxygenator, bubbles different in size and formwere put into the blood. Using a bubble detector, measurement was madeof the amount of bubbles in the blood flowing our of the blood outletport under the conditions shown below. The result is shown in Table 2.

Bubble detection time: 1 minute

Bubble count: the bubbles measured by the bubble detector wereclassified according to classes at a bubble-size interval of 10 μM, tofind the classified totals of bubbles.

TABLE 2 Bubble Performance Test (Bubble count detected by bubbledetector) Flow rate of blood Q Bubble size [μm] Model [mL/min] 41-5051-60 61-70 71-80 81-90 91-100 Example 1 Model 1 7000 0 0 0 0 0 0 Model2 5000 0 0 0 0 0 0 Model 3 1500 0 0 0 0 0 0 Example 2 Model 4 7000 1 0 00 0 0 Comparative Model 5 RX25 7000 32 56 34 9 1 0 example 1 Model 6RX15 5000 61 40 15 3 0 0 Model 7 RX05 1500 106 72 44 27 5 0 ComparativeModel 8 7000 13 9 7 3 0 0 example 2 [unit: bubble count]

As shown in Table 2, the oxygenators (models 1-4) in Examples 1 and 2were observed to have a high bubble removal performance. Particularly,the oxygenators (models 1-3) in Example 1, having a passage enlargementformed by the first and second enlargements, possesses an extremely highbubble removal performance in which no bubbles, regardless of bubblesize, were observed at the blood outlet port.

It is to be recognized that the principles, embodiments and modes ofoperation have been described in the foregoing specification, but theinvention which is intended to be protected is not to be construed aslimited to the particular embodiments disclosed. Further, theembodiments described herein are to be regarded as illustrative ratherthan restrictive. Variations and changes may be made by others, andequivalents employed, without departing from the spirit of the presentinvention. Accordingly, it is expressly intended that all suchvariations, changes and equivalents which fall within the spirit andscope of the present invention as defined in the claims, be embracedthereby.

1. A method of performing gas exchange for blood comprising: introducingblood into a housing in which are positioned a plurality of hollow fibermembranes each having a lumen so that the blood flows exteriorly of thehollow fiber membranes; introducing gas into the lumens of the hollowfiber membranes to subject the blood flowing exteriorly of the hollowfiber membranes to gas exchange with the gas flowing through the lumensof the hollow fiber membranes; removing bubbles in the blood while theblood is in the housing and after the blood has been subjected to thegas exchange; decelerating the blood from which bubbles have beenremoved as the blood approaches a blood outlet port in the housing; anddischarging from the housing by way of the blood outlet port the bloodwhich has been decelerated.
 2. A method according to claim 1, whereinthe blood is decelerated by flowing along a passage enlargement adjacentthe blood outlet port possessing an increased passage cross-sectionalarea.
 3. A method according to claim 1, further comprising dischargingbubbles which have been removed from the blood by way of lumens inhollow fiber membranes forming a gas outlet hollow fiber membrane layer.4. A method according to claim 1, further comprising discharging bubbleswhich have been removed from the blood by way of the lumens of thehollow fiber membranes.